The present application claims priority to Japanese Application No. P10 188672 filed Jul. 03, 1998, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a dry etching apparatus used in fabrication of super LSIs, and so forth, for micro processing of a pattern by exciting and activating a gas with electric-discharge plasma to make it interact with a substance on a wafer and then evacuating it, and also relates to a method for dry-etching a substrate.
2. Description of the Related Art
Along with progressive miniaturization of semiconductor devices, for the purpose of enabling processing of finer patterns than those heretofore realized dy dry etching apparatuses as their manufacturing apparatuses, further improvements are under progress with employment of a method ensuring highly even electric discharge of a plasma and realization of high-speed evacuation. Together with improvements of such etching techniques, reduction of particles for preventing defects in micro-sized patterns during processing is an important factor required in manufacturing apparatuses. In order to prevent products of reaction as a major source of particles from accumulating in a reaction chamber during processing, there is a movement toward reducing parts in the reaction chamber and simplifying the flow of reaction products.
An example of conventional dry etching apparatuses is shown in FIG. 1. Shown here is a substrate susceptor by reference numeral 101. The substrate susceptor 101 mainly comprises a lower electrode 111, an annular focus ring 112, and so on. The lower electrode 111 has formed on its top surface a groove 113 for a cool gas, and the groove 113 is connected to a cool gas supply/exhaust line 114. Helium gas, for example, is used as the cool gas. Provided inside the lower electrode 111 are a cooling tank 115 containing a refrigerant and a wafer push-up mechanism 116 located in a central position. The lower electrode 111 is connected to a high-frequency power source 118 via a capacitor 119.
Further referring to FIG. 1, reference numeral 102 denotes an upper end portion of the reaction chamber. The upper end portion 102 of the reaction chamber is dome-shaped, and a coil 123 fitting on the outer circumferential surface of the dome-shaped upper end portion 102 is connected with its one end to a high-frequency power source 121 via a capacitor 122 and with the other end to the ground.
Still referring to FIG. 1, reference numeral 110 denotes a wafer to be processed by etching. The wafer 110 is transported by a carrier arm, not shown, and put on the substrate susceptor 101 at a position where the inner circumferential surface of the focus ring 112 functions as positional definition thereof. Additionally, etching gas inlets and exhaust gas outlets, not shown, are provided at lateral locations relative to the position where the wafer 110 lie. A predetermined etching gas is supplied through the inlets into the reaction chamber, and electric-discharge plasma is generated in the reaction chamber held under a predetermined low pressure and a predetermined temperature held in the reaction chamber by applying high-frequency voltages to the lower electrode 111 and the high-frequency coil 123 from high-frequency power sources 118, 121. The electric-discharge plasma excites and activates the etching gas to have it interact with a substance on the wafer and thereby invite etching. In this process, flows of the etching gas from the inlets move along the contour of the dome-shaped upper end portion 102 as shown by arrows in FIG. 1 first to the central portion, there turn their directions to move downward through the plasma region 133, then turn their directions near the surface of the wafer 110 to move laterally while licking the surface of the wafer 110, and finally move to the exhaust gas outlets.
In the above-introduced dry etching apparatus using electric-discharge plasma, a complex electric-discharge mechanism occupies the space just above the wafer, and the etching gas inlets are located at lateral positions relative to the wafer. Therefore, the etching gas circulates through the plasma region 133. As a result, reaction products which should be discharged by flows of the gas are re-dissociated by the plasma and adhere to any in the reaction chamber. More specifically, stagnation occurs in the gas flows at the stepped portion of the focus ring 112 surrounding the wafer 110, and reaction products accumulate there as shown at 132 in FIG. 1 and may cause generation of dust due to re-dissociation of the reaction products 132.
For the purpose of overcoming the problem, namely, preventing re-adhesion of reaction products, there is proposed a dry etching apparatus smoothing gas flows by removing any step disturbing evacuation of the gas, like that on the focus ring, from the portion around the wafer. FIG. 2 shows such a dry etching apparatus removing the focus ring to make a flat plane. In FIG. 2, elements and parts common to those of the apparatus shown in FIG. 1 are labeled with common reference numerals.
In case of the dry etching apparatus shown in FIG. 2, the upper end portion 102 of the reaction chamber is configured as a flat plate, and the coil 123 fitting on the outer circumferential surface of the flat upper end portion 102 is connected with its one end to the high-frequency power source 121 via the capacitor 122 and with the other end to the ground. Additionally, an upper electrode 124 is attached onto the flat upper end portion 102. The upper electrode 124 has formed diffusion holes 125 distributed all over its area to introduce an etching gas, and these diffusion holes 125 are connected to an etching gas inlet tube 126.
In the dry etching apparatus having the above-explained structure, the etching gas supplied through the diffusion holes 125 falls down from the respective diffusion holes 125 through the plasma region 133 to the proximity of the wafer, there changes its direction to move transversely while licking the surface of the wafer 110, and finally moves to the exhaust gas outlets.
However, the dry etching apparatus shown in FIG. 2 also fails to remove the possibility that not a small amount of reaction products accumulate along the perimeter of the substrate susceptor 101 around the wafer 110 as shown at 132 in FIG. 2, and dust is generated due to re-dissociation of the reaction products 132. On the other hand, since this apparatus removes any step like that made by the focus ring for the purpose of making smooth gas flows, it has no means to mechanically determine the setting position of the wafer 110 transported there, and therefore involves the possibility that the wafer is offset from the proper setting position as shown by the broken line and an arrow in FIG. 2, for example, and thereby disables its transport. As reviewed above, conventional dry etching apparatuses were compelled to determine the structure of the substrate susceptor so as to preferentially select one at the cost of the other of the requirements, namely, preventing generation of particles in the reaction chamber and ensuring reliable transport of wafers, and no dry etching apparatus satisfying both these requirements has been proposed heretofore.
It is therefore an object of the invention to provide a dry etching apparatus capable of minimizing adhesion of reaction products, or any other matters, which will become a source of particles, and simultaneously ensuring stable transport, and to provide a method for dry-etching substrates by using the dry etching apparatus.
According to the invention of the second claim, there is provided a dry etching apparatus characterized in that a substrate susceptor has a portion for contact with a wafer, having a diameter not larger than the diameter of the wafer, and no element is provided in any level higher than the top surface of the wafer and in the same level as the bottom surface of the wafer around the wafer.
According to the invention, there is further provided a method for dry-etching a substrate by using the dry etching apparatus.
In the present invention, a susceptor cover is attached to a substrate susceptor to shape it into a tapered contour, and no other element is positioned around a wafer support plane to ensure a flatness. Additionally, a predetermined distance is provided between the side wall of the reaction chamber and the substrate susceptor, and exhaust gas outlets of the etching gas are located in a lower level in the reaction chamber, to reliably prevent opposite flows of the gas toward the electric discharge plasma. Therefore, the etching gas smoothly moves toward the exhaust gas outlets at a lower level in the reaction chamber, and products generated by interaction with the wafer and products of sputtering of members of the apparatus do not accumulate near the wafer although it may accumulate near the exhaust gas outlets located in a lower level in the reaction chamber. Therefore, adhesion of such products of interaction or sputtering onto the wafer is minimized.
Additionally, in the present invention, four columnar pins made of an insulating material and four cylinders for extending and contracting the pins are provided near the perimeter of the wafer support plane in intervals of 90 to form a wafer positioning mechanism, and these four columnar pins are moved to extend to a level higher than the wafer support plane and thereby engage with the side edge of the wafer only upon setting and removing the wafer, and are withdrawn into the substrate susceptor during etching. Therefore, the positioning mechanism prevents a positional offset of the wafer upon setting and removing same without adversely affect the etching quality of the wafer.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.